This invention relates to a transportation system and specifically to an apparatus which supplies a vehicle command signal having constraints or limitations for controlling vehicle movement to provide riding comfort and prompt service.
Many types of command signals have been utilized within motor control circuits for comparison with signals which represent the actual operation of the motor and the objects they control to develop an error signal to appropriately energize the motor. Such closed loop control systems have sensed various facets of the operation to develop the operational responsive signals such as, for example, the position of the motor drive shaft or of the object which it controls, the speed of drive shaft rotation or of the object it controls, or the counter-electromotive force (Cemf) sensed at the motor armature circuit. In many prior closed loop control systems, the absence of an error signal has indicated that the motor is operating in accordance with the motor command signal which is thus equal to the magnitude of the motor responsive signal. A difference existing between the command and operational responsive signals indicates that the commanded object is either operating too fast or too slow or is not at a proper position and thus an error signal is developed to correspondingly speed up or slow down the drive motor.
Some prior transportation systems have not precisely defined the commanded velocity, acceleration and rate of change of acceleration or "jerk" required by their pattern or command signal generator. Sych systems have thus experienced relatively sharp transitions in velocity and acceleration which have been tolerable because of the sluggish response of the equipment operated by the controlled motor. With some operating equipment having slow responses, such sharp transitions are sometimes desired in the interest of expediting the output of the motor.
Transportation systems such as elevators require smooth riding characteristics to provide a comfortable ride for passengers and yet it is desirable to minimize the floor to floor time to provide high quality service. In such a system, it is desirable to provide smooth accelerating characteristics and high speed service between floors by maintaining limitations upon the acceleration and rate of change of acceleration commonly referred to as "jerk." It is further desirable to impose a limitation upon the maximum permissible velocity for the controlled vehicle to maintain the vehicle speed within the safe operating limits of the equipment to ensure passenger safety.
Some prior transportation systems have imposed maximum velocity, acceleration and rate of change of acceleration limitations utilizing timed, stepped command signals to control the motor energization. Such systems have frequently permitted the motor to operate sluggishly to mask or conceal the stepped input to provide the desired smooth riding characteristics. The systems providing stepped command signals have not generally provided the precise control over a continuous accelerating and decelerating range and have generally required auxiliary positioning equipment to exact a precise stop at a landing or floor.
Many transportation systems continually sense the vehicle position and provide signals directly proportional thereto in order to accurately control the vehicle movement. Such position responsive controls have been in many cases believed to be required, such as in elevator systems, and particularly to provide a desirable deceleration of the vehicle in order to accurately stop at a landing.
One known system has utilized a position as a function of time command pattern voltage having limitations in maximum obtainable velocity, acceleration and rate of change of acceleration which is compared with a car position voltage to produce a position error signal to control an elevator operation through a Ward-Leonard type motor-generator set, such as disclosed in U.S. Pat. Nos. 3,523,232 and 3,612,220, issued to Hall et al on Aug. 4, 1970 and Oct. 12, 1971, respectively. Such a system as disclosed in the Hall et al patents computes the command pattern voltage by developing a potential difference between an initial car position voltage and a call request voltage while the command pattern is transferred to a signal based upon the car distance from the destination during the period of maximum negative acceleration to achieve the requisite landing accuracy.
Another known system accelerates an elevator car at the same predetermined rate for any length of trip solely as a function of time in response to the operation of a time-controlled speed dictation signal-generating device but decelerates as a function of distance in accordance with the operation of a distance-controlled speed dictation signal generating device, such as disclosed in U.S. Pat. No. 3,552,524, issued to Benjamin et al on Jan. 5, 1971.